Conductive In Situ Reduced Graphene Oxide-Silk Fibroin Bionanocomposites

This research paper describes the fabrication of bionanocomposites (BNCs) based on silk fibroin (SF) and reduced graphene oxide (rGO). The recorded UV-visible (UV-vis) spectra of the sample confirm the reduction of GO to rGO in SF by showing a plasmon resonance band within the wavelength range of 261-268 nm. The X-ray diffraction (XRD) peak at 11.6° corresponding to the GO intensity decreases with increasing reaction time, resulting in rGO in the SF host matrix. The morphological behavior of the SF-rGO BNCs is scrutinized using scanning electron microscopy (SEM), and the images clearly indicate the existence of rGO within the matrix. The increasing amount of GO in the SF shows broken graphene sheets, which can increase the surface roughness and establish a strong physical contact between the SF and rGO nanosheets. The high-resolution transmission electron microscope (HR-TEM) image of the bionanocomposite showed that the formed rGO encompassments of fewer layers are stacked, each with fewer wrinkles and folding. The Raman spectroscopy confirmed the formation of rGO by showing the increased intensity ratio of D to G band (I D/I G) in the bionanocomposite samples. The rGO effect on the electrical conductivity is measured, and the results show that DC conductivity increases from 1.28 × 10-9 to 82.4 × 10-9 S/cm with an increase in the GO content in the SF biopolymer. The investigations demonstrate loss of the insulation property and improved conducting behavior of the SF biopolymer.

Recent progress in silk fibroin-based flexible electronics

With the rapid development of the Internet of Things (IoT) and the emergence of 5G, traditional silicon-based electronics no longer fully meet market demands such as nonplanar application scenarios due to mechanical mismatch. This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials. In recent decades, biological materials with outstanding biocompatibility and biodegradability, which are considered some of the most promising candidates for next-generation flexible electronics, have received increasing attention, e.g., silk fibroin, cellulose, pectin, chitosan, and melanin. Among them, silk fibroin presents greater superiorities in biocompatibility and biodegradability, and moreover, it also possesses a variety of attractive properties, such as adjustable water solubility, remarkable optical transmittance, high mechanical robustness, light weight, and ease of processing, which are partially or even completely lacking in other biological materials. Therefore, silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics, particularly for wearable and implantable devices. Furthermore, in recent years, more attention has been paid to the investigation of the functional characteristics of silk fibroin, such as the dielectric properties, piezoelectric properties, strong ability to lose electrons, and sensitivity to environmental variables. Here, this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advanced works in which silk fibroin serves as functional components. Additionally, the challenges and future development of silk fibroin-based flexible electronics are summarized. (1) This review focuses on silk fibroin serving as active functional components to construct flexible electronics. (2) Recent representative reports on flexible electronic devices that applied silk fibroin as fundamental supporting components are summarized. (3) This review summarizes the current typical silk fibroin-based materials and the corresponding advanced preparation technologies. (4) The current challenges and future development of silk fibroin-based flexible electronic devices are analyzed.

High-Performance Luminescent Solar Concentrators Based on Poly(Cyclohexylmethacrylate) (PCHMA) Films

In this study, we report on the use of poly(cyclohexylmethacrylate) (PCHMA) as an alternative to the commonly used poly(methylmethacrylate) (PMMA) for the design of efficient luminescent solar concentrators (LSCs). PCHMA was selected due to its less polar nature with respect to PMMA, a characteristic that was reported to be beneficial in promoting the fluorophore dispersibility in the matrix, thus maximizing the efficiency of LSCs also at high doping. In this sense, LSC thin films based on PCHMA and containing different contents of Lumogen F Red 305 (LR, 0.2–1.8 wt%) demonstrated optical efficiencies (η_opt) comprising between 9.5% and 10.0%, i.e., about 0.5–1% higher than those collected from the LR/PMMA systems. The higher LR/polymer interactions occurred using the PCHMA matrix maximized the solar harvesting characteristics of the fluorophore and limited the influence of the adverse dissipative phenomena on the fluorophore quantum efficiency. These effects were also reflected by varying the LSC film thickness and reaching maximum η_opt of about 11.5% in the case of PCHMA films of about 30 µm.

Luminescent Solar Concentrators from Waterborne Polymer Coatings

This study reports for the first time the use of waterborne polymers as host matrices for luminescent solar concentrators (LSCs). Notably, three types of waterborne polymer dispersions based either on acrylic acid esters and styrene (Polidisp® 7602), acrylic and methacrylic acid esters (Polidisp® 7788) or aliphatic polyester-based polyurethane (Tecfin P40) were selected as amorphous coatings over glass substrates. Water soluble Basic Yellow 40 (BY40) and Disperse Red 277 (DR277) were utilized as fluorophores and the derived thin polymer films (100 μm) were found homogeneous within the dye range of concentration investigated (0.3–2 wt.%). The optical efficiency determination (ηopt) evidenced LSCs performances close to those collected from benchmark polymethylmethacrylate (PMMA) thin films and Lumogen Red F350 (LR) with the same experimental setup. Noteworthy, maximum ηopt of 9.5 ± 0.2 were recorded for the Polidisp® 7602 matrix containing BY40, thus definitely supporting the waterborne polymer matrices for the development of high performance and cost-effective LSCs.

Towards Efficient Spectral Converters through Materials Design for Luminescent Solar Devices

Single-junction photovoltaic devices exhibit a bottleneck in their efficiency due to incomplete or inefficient harvesting of photons in the low- or high-energy regions of the solar spectrum. Spectral converters can be used to convert solar photons into energies that are more effectively captured by the photovoltaic device through a photoluminescence process. Here, recent advances in the fields of luminescent solar concentration, luminescent downshifting, and upconversion are discussed. The focus is specifically on the role that materials science has to play in overcoming barriers in the optical performance in all spectral converters and on their successful integration with both established (e.g., c-Si, GaAs) and emerging (perovskite, organic, dye-sensitized) cell types. Current challenges and emerging research directions, which need to be addressed for the development of next-generation luminescent solar devices, are also discussed.

Cellulose nanocrystals as host matrix and waveguide materials for recyclable luminescent solar concentrators

We report the use of an ecofriendly and recyclable CNC material as the host matrix for luminescent solar concentrator applications.

Natural Silk as a Photonics Component: a Study on Its Light Guiding and Nonlinear Optical Properties

Silk fibers are expected to become a pathway to biocompatible and bioresorbable waveguides, which could be used to deliver localized optical power for various applications, e.g., optical therapy or imaging inside living tissue. Here, for the first time, the linear and nonlinear optical properties of natural silk fibers have been studied. The waveguiding properties of silk fibroin of largely unprocessed Bombyx mori silkworm silk are assessed using two complementary methods, and found to be on the average 2.8 dB mm(-1). The waveguide losses of degummed silk are to a large extent due to scattering from debris on fiber surface and helical twisting of the fiber. Nonlinear optical microscopy reveals both configurational defects such as torsional twisting, and strong symmetry breaking at the center of the fiber, which provides potential for various nonlinear applications. Our results show that nonregenerated B. mori silk can be used for delivering optical power over short distances, when the waveguide needs to be biocompatible and bioresorbable, such as embedding the waveguide inside living tissue.

A lysinated thiophene-based semiconductor as a multifunctional neural bioorganic interface

Lysinated molecular organic semiconductors are introduced as valuable multifunctional platforms for neural cells growth and interfacing. Cast films of quaterthiophene (T4) semiconductor covalently modified with lysine-end moieties (T4Lys) are fabricated and their stability, morphology, optical/electrical, and biocompatibility properties are characterized. T4Lys films exhibit fluorescence and electronic transport as generally observed for unsubstituted oligothiophenes combined to humidity-activated ionic conduction promoted by the charged lysine-end moieties. The Lys insertion in T4 enables adhesion of primary culture of rat dorsal root ganglion (DRG), which is not achievable by plating cells on T4. Notably, on T4Lys, the number on adhering neurons/area is higher and displays a twofold longer neurite length than neurons plated on glass coated with poly-l-lysine. Finally, by whole-cell patch-clamp, it is shown that the biofunctionality of neurons cultured on T4Lys is preserved. The present study introduces an innovative concept for organic material neural interface that combines optical and iono-electronic functionalities with improved biocompatibility and neuron affinity promoted by Lys linkage and the softness of organic semiconductors. Lysinated organic semiconductors could set the scene for the fabrication of simplified bioorganic devices geometry for cells bidirectional communication or optoelectronic control of neural cells biofunctionality.

A nanostructured conductive bio-composite of silk fibroin-single walled carbon nanotubes

Silk fibroin (SF), a protein core fibre from the silkworm Bombyx mori, has huge potential to become a sustainable, biocompatible, and biodegradable material platform that can pave the way towards the replacement of plastic in the fabrication of bio-derived materials for a variety of technological and biomedical applications. SF has remarkable mechanical flexibility, controllable biodegradability, biocompatibility and is capable of drug/doping inclusion, stabilization and release. However, the dielectric properties of SF limit its potential as a direct bioelectronic interface in biomedical devices intended to control the bioelectrical activity of the cell for regenerative purposes. In this work, a novel wet templating method is proposed to generate nanostructured, conductive Silk Fibroin (SF) composite films. We combine the unusual properties of SF, such as its mechanical properties, its convenience and biocompatibility with the electrical conductivity and stiffness of Single Walled Carbon Nanotubes (SWCNTs). The presented SF-SWCNT composite displays a periodic architecture where SWCNTs are regularly and homogeneously distributed in the SF protein matrix. The morphological and chemo-physical properties of the nanocomposite are analysed and defined by SEM, Raman Spectroscopy, ATR-IR, UFM and contact angle analyses. Notably, the SF-SWCNT composite film is conductive, showing additional functionality compared to the dielectric properties of the bare SF film. Finally, SF-SWCNT is biocompatible and enables the growth of primary rat Dorsal Root Ganglion (DRG) neurons. Collectively our results demonstrate that the nanostructured, conductive, robust and biocompatible SF-SWCNT composite can be fabricated using a wet templating method, paving the way towards the fabrication and development of silk-based electronic devices for use in bioelectronic and biomedical applications.

Integration of a silk fibroin based film as a luminescent down-shifting layer in ITO-free organic solar cells

A bio-derived silk-fibroin film doped with a luminescent dye and its application as luminescent down-shifting layer in organic solar cells.